In Gethenian society, Estraven is a land-name. It means "one who comes from Estre," sort of like being called "da Vinci."
So, the Estraven from this story is not the same Estraven we know and love from Ai's story. His name is Arek although he is sometimes called Estraven because it's his birthplace.
Still, the name is meant to clue us in that he connects somehow to Ai's Estraven. If not literally, then metaphorically or perhaps both.
Okay, everyone on board? Let's get this chapter rolling.
So, there's this blood feud between two lands, the Domain of Stok and the Domain of Estre.
One day, the young Lord of Estre is skiing over Icefoot Lake when he falls through some rotten ice.
He manages to free himself from the frigid water, but he's not out of trouble, yet. He wanders around, slowly freezing to death, until he comes to a small house.
Like a pro, the house's owner quickly gets the young lord out of his wet clothes and next to a fire.
If you think this sounds like the set up to a romantic comedy, you'd be right. Except about the comedy part.
Turns out, the owner is Therem of Stok, mortal enemy of Arek, the Lord of Estre. They immediately fall in love with each other Romeo and Juliet-style.
They spend a few days together in the cabin. Then a party of Stok men comes into the cabin. Evidently, no one taught them to knock first.
They see Arek and kill him, effectively ending the honeymoon.
Therem tells the men to take Arek's body to Estre for burial. The men just drop the body off somewhere, because they aren't stupid enough to take the person they killed to his powerful and presumably ticked-off father.
But when Therem discovers their trickery, he has them banished. Then Therem disappears as quickly as Tom Green's career. Who's Tom Green?
In the Domain of Estre, they search for Arek's body but find nothing. One day, a man arrives with a newborn baby. Surprise! It's Therem, son of Arek of Estre.
The Lord of Estre agrees to raise the child and even keeps the name Therem. How they can tell it's actually Arek's son is anybody's guess. Maybe he had his father's nose or something.
Years pass, and the baby grows up. He's named the heir of Estre, an idea the Lord's other children don't really cotton to. They try to ambush Therem, but the boy is apparently a Bruce-Lee-level fighter, as he kills all three of them.
Wounded and getting weaker, Therem sees, guess what, a cabin. It's abandoned, so the boy enters it and collapses on the floor.
A man comes to the cabin and tends Therem's wounds.
When Therem comes to, he realizes that the man is Therem of Stok, his mother, er father, uh…birth parent?
The two reach a peace agreement with each other. When Therem of Estre becomes king, he makes peace between the lands as well.